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**Short-circuit impedance, also known as voltage impedance, is an important reference for measuring the parallel operation and economic efficiency of transformers.**

Transformer short-circuit impedance and load impedance using transformer no-load and on-load tester for measurement.When testing short-circuit impedance, the secondary side of the transformer short circuit,apply voltage to the primary side,and converted into a percentage of the rated voltage, that is, short-circuit impedance. on-load impedance test method is exactly the opposite with short-circuit impedance test method.Need to apply voltage on the secondary side, the primary side short circuit.

The boosting method is gradual, and the voltage is gradually increase from the LV side until the current on the HV side reaches the rated value.

**The effect of impedance voltage on the transformer**

The greater the impedance voltage of the transformer, the smaller the short-circuit current flowing through the transformer,he lighter the impact on the transformer.So currently the minimum short-circuit impedance value is required when the transformer is manufactured.But the impedance voltage of the transformer increases, which has higher requirements for the manufacturing process;

When the transformer is fully loaded, the level of the short-circuit impedance has a certain impact on the level of the secondary side output voltage.If the short-circuit impedance is small, the voltage drop is small.If the short-circuit impedance is large, the voltage drop is large. When the transformer load is short-circuited, the short-circuit impedance is small, the short-circuit current is large, and the electrical power of the transformer is large. If the short-circuit impedance is large, the short-circuit current is small, and the electrical power of the transformer is small.

**The required value of the transformer impedance voltage**

The test results of the short-circuit impedance and load impedance of the transformer differ from the factory value in the range of ±5%, and the difference with the average value of the three-phase or three-phase group is within the range of ±2%.